Removable electron multileaf collimator

ABSTRACT

A removable electron collimator for use in collimating an electron beam in a radiation therapy device is provided, where the collimator includes drive electronics, removably mounted on an exterior of an accessory tray of the radiation therapy device. The electron collimator also includes a plurality of leaves positionable by the drive electronics to move across a path of the electron beam, the plurality of leaves removably mounted on the accessory tray of the radiation therapy device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to commonly owned U.S. patentapplication Ser. No. ______, filed Jul. 20, 2001 (on even dateherewith), Attorney Docket No. 2001P13116US for “AUTOMATED DELIVERY OFTREATMENT FIELDS”, and U.S. patent application Ser. No. ______, filedJul. 20, 2001 (on even date herewith), Attorney Docket No. 2001P13113USfor “VERIFICATION OF ELECTRON TREATMENT FIELDS”, the contents of each ofwhich are incorporated by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to radiation therapydevices, and more particularly, to a removable electron multileafcollimator for use in a radiation therapy device.

[0004] 2. Description of the Related Art

[0005] Conventional radiation therapy typically involves directing aradiation beam at a tumor in a patient to deliver a predetermined doseof therapeutic radiation to the tumor according to an establishedtreatment plan. This is typically accomplished using a radiation therapydevice such as the device described in U.S. Pat. No. 5,668,847 issuedSep. 16, 1997 to Hernandez, the contents of which are incorporatedherein for all purposes.

[0006] The radiotherapy treatment of tumors involves three-dimensionaltreatment volumes which typically include segments of normal, healthytissue and organs. Healthy tissue and organs are often in the treatmentpath of the radiation beam. This complicates treatment, because thehealthy tissue and organs must be taken into account when delivering adose of radiation to the tumor. While there is a need to minimize damageto healthy tissue and organs, there is an equally important need toensure that the tumor receives an adequately high dose of radiation.Cure rates for many tumors are a sensitive function of the dose theyreceive. Therefore, it is important to closely match the radiationbeam's shape and effects with the shape and volume of the tumor beingtreated.

[0007] Both primary photon and primary electron beams may be used inradiation therapy. Accordingly, many existing radiation therapy devicesinclude the ability to generate and deliver both photon and electronbeams. Currently, clinical practice requires substantial manualintervention to use conformal electron treatment. Conformal photonfields typically are shaped using one or more collimating devicespositioned between the source and the treatment area. Many of thesephoton beam collimating devices may be positioned automatically todeliver a desired photon field shape to a treatment area on a patient.Little manual intervention is required to administer photon radiationtherapy.

[0008] Primary electrons are currently used on approximately 30% of allpatients who undergo radiation therapy. Electron fields delivered viaradiation therapy devices are typically shaped using either anoff-the-shelf electron applicator (either rectangular or circular incross-section) or a custom cutout formed of Cerrobend®. Both of thesebeam shaping methods have limitations. Off-the-shelf electronapplicators often unnecessarily irradiate portions of healthy tissue,since they do not precisely conform to the target. Custom cutouts formedof Cerrobende are highly conformal, but are costly to make, store andrequire special quality assurance. The Cerrobend® material may alsorequire special handling because of the potentially toxic metalsinvolved. Each of these approaches to electron field shaping also sufferin that they can be inefficient to use. A radiation therapist deliveringa prescribed treatment must repeatedly enter the treatment room duringtreatment to insert the proper cutout for each field in the therapy.This is not only inefficient, but it effectively precludes the deliveryof treatments which require electron field modulation in both intensityand energy at a single gantry position.

[0009] Oncologists would like to have the ability to prescribe mixedbeam treatments which include the application of modulated electron andphoton fields. With the exception of a few highly specialized andexpensive devices, existing radiation therapy devices are unable toeffectively provide such mixed beam treatments. Although existingradiation therapy devices do have the ability to deliver both electronand photon beams, the devices are unable to provide mixed beamtreatments without requiring the repeated replacement and manualintervention by a therapist during treatment. It would be desirable toprovide a radiation therapy device which is able to support mixed beamtreatments where both photon and electron beams may be used in a singlecourse of treatment and where the electron beam may be modulated in bothintensity and energy without intervention by a radiation therapist. Itwould also be desirable to provide a system and method that allows theelectron collimator assembly to be readily installed and removed asdesired.

SUMMARY OF THE INVENTION

[0010] To alleviate the problems inherent in the prior art, and to allowthe efficient and effective delivery of photon, electron, and mixed beamradiation therapy, embodiments of the present invention provide a systemand method for use of a removable electron collimator.

[0011] According to one embodiment of the present invention, a radiationtherapy device is provided which includes a radiation source positionedto direct a beam along a beam path toward a treatment area. The systemincludes a treatment head containing a first collimator controllable toselectively collimate the beam, and a second collimator removablypositioned between the first collimator and the treatment area andcontrollable to selectively collimate the beam. In one embodiment, thesecond collimator is removably mounted on an accessory tray of theradiation therapy device. According to one embodiment, the firstcollimator is used to collimate a photon beam generated by the source,while the second collimator is used to collimate an electron beamgenerated by the source.

[0012] According to one embodiment of the present invention, an electroncollimator for use in collimating an electron beam in a radiationtherapy device is provided, where the collimator includes driveelectronics, removably mounted on an exterior of an accessory tray ofthe radiation therapy device. The electron collimator also includes aplurality of leaves positionable by the drive electronics to move acrossa path of the electron beam, the plurality of leaves removably mountedon the accessory tray of the radiation therapy device.

[0013] The present invention is not limited to the disclosed preferredembodiments, however, as those skilled in the art can readily adapt theteachings of the present invention to create other embodiments andapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The exact nature of this invention, as well as its objects andadvantages, will become readily apparent from consideration of thefollowing specification as illustrated in the accompanying drawings, inwhich like reference numerals designate like parts throughout thefigures thereof, and wherein:

[0015]FIG. 1 is diagram illustrating a radiation therapy device;

[0016]FIG. 2 is a block diagram illustrating portions of the radiationtherapy device of FIG. 1 according to one embodiment of the presentinvention;

[0017]FIG. 3 is a diagram illustrating a treatment head for use in aradiation therapy device according to one embodiment of the presentinvention; and

[0018]FIG. 4 is a diagram illustrating a collimator for use in aradiation therapy device according to one embodiment of the presentinvention.

DETAILED DESCRIPTION

[0019] The following description is provided to enable any personskilled in the art to make and use the invention and sets forth the bestmodes contemplated by the inventor for carrying out the invention.Various modifications, however, will remain readily apparent to thoseskilled in the art.

[0020] Turning now to the drawings and, with particular attention toFIG. 1, a radiation therapy device 10 pursuant to embodiments of thepresent invention is shown. According to one embodiment of the presentinvention, radiation therapy device 10 includes a beam shielding device(not shown) within a treatment head 24, a control unit in a housing 30and a treatment unit 32. An accessory tray 25 is mounted to an exteriorof treatment head 24. Accessory tray 25, in one embodiment, isconfigured to receive and securely hold attachments used during thecourse of treatment planning and treatment (such as, for example,reticles, wedges, or the like).

[0021] Radiation therapy device 10 includes a gantry 26 which can beswiveled around a horizontal axis of rotation 20 in the course of atherapeutic treatment. Treatment head 24 is fastened to a projection ofthe gantry 26. A linear accelerator (not shown) is located inside gantry26 to generate the high energy radiation required for the therapy. Theaxis of the radiation bundle emitted from the linear accelerator and thegantry 26 is designated by beam path 12. Electron, photon or any otherdetectable radiation can be used for the therapy. Embodiments of thepresent invention permit the controlled delivery of both primaryelectron and primary photon beams to a treatment zone 18 during thecourse of a prescribed treatment.

[0022] During a course of treatment, the radiation beam is trained ontreatment zone 18 of an object 22, for example, a patient who is to betreated and whose tumor lies at the isocenter of the gantry rotation.The plates or leaves of the beam shielding device within the treatmenthead 24 are substantially impervious to the emitted radiation. Thecollimator leaves or plates are mounted between the radiation source andthe patient in order to delimit (conform) the field. Areas of the body,for example, healthy tissue, are therefore subject to as littleradiation as possible and preferably to none at all. The plates orleaves are movable such that the distribution of radiation over thefield need not be uniform (one region can be given a higher dose thananother). Furthermore, the gantry can be rotated so as to allowdifferent beam angles and radiation distributions without having to movethe patient.

[0023] According to one embodiment of the present invention, severalbeam shaping devices are used to shape radiation beams directed towardtreatment zone 18. In one embodiment, a photon collimator and anelectron collimator are provided. Each of these collimators, as will bedescribed further below, may be separately controlled and positioned toshape beams directed at treatment zone 18. According to one embodiment,the photon collimator (not shown in FIG. 1) is contained withintreatment head 24 and the electron collimator (not shown in FIG. 1) isremovably mounted on accessory tray 25.

[0024] Radiation therapy device 10 also includes a central treatmentprocessing or control unit 32 which is typically located apart fromradiation therapy device 10. Radiation therapy device 10 is normallylocated in a different room to protect the therapist from radiation.Treatment unit 32 includes a processor 40 in communication with anoperator console 42 (including one or more visual display units ormonitors) and an input device such as a keyboard 44. Data can be inputalso through data carriers such as data storage devices or averification and recording or automatic setup system. More than onecontrol unit 32, processor 40, and/or operator console 42 may beprovided to control radiation therapy device 10.

[0025] Treatment processing unit 32 is typically operated by a therapistwho administers actual delivery of radiation treatment as prescribed byan oncologist. Therapist operates treatment processing unit 32 by usingkeyboard 44 or other input device. The therapist enters data definingthe radiation dose to be delivered to the patient, for example,according to the prescription of the oncologist. The program can also beinput via another input device, such as a data storage device. Variousdata can be displayed before and during the treatment on the screen ofoperator console 42.

[0026] Embodiments of the present invention permit the delivery of bothprimary electron and primary photon beams to treatment zone 18 duringthe course of a prescribed treatment. Embodiments of the presentinvention permit the creation and control of both photon and electronradiation beams which closely match the shape and size of treatment zone18.

[0027] Referring now to FIG. 2, a block diagram is shown depictingportions of a radiation therapy device 10 and treatment unit 32according to one embodiment of the present invention. In particular,treatment delivery elements of a radiation therapy device are shown,which may be configured in radiation therapy device 10 and treatmentunit 32 as depicted in FIG. 1. The treatment delivery elements include acomputer 40, operatively coupled to an operator console 42 for receivingoperator control inputs and for displaying treatment data to anoperator. Operator console 42 is typically operated by a radiationtherapist who administers the delivery of a radiation treatment asprescribed by an oncologist. Using operator console 42, the radiationtherapist enters data that defines the radiation to be delivered to apatient.

[0028] Mass storage device 46 stores data used and generated during theoperation of the radiation therapy device including, for example,treatment data as defined by an oncologist for a particular patient.This treatment data is generated, for example, using a treatmentplanning system 60 which may include manual and computerized inputs todetermine a beam shape prior to treatment of a patient. Treatmentplanning system 60 is typically used to define and simulate a beam shaperequired to deliver an appropriate therapeutic dose of radiation totreatment zone 18.

[0029] Data defining the beam shape and treatment are stored, e.g., inmass storage device 46 for use by computer 40 in delivering treatment.According to one embodiment of the present invention, treatment planningmay include activities which occur prior to the delivery of thetreatment, such as the generation of treatment data defining a photontreatment, an electron treatment, and/or a mixed beam treatment.Embodiments of the present invention permit the use of mixed beamtreatments without the need for extended disruptions to install electronapplicators or other shielding devices. Further, embodiments of thepresent invention permit field shaping of electron beams during atreatment in a device which also permits field shaping of photon beamsduring a treatment.

[0030] Although a single computer 40 is depicted in FIG. 2, thoseskilled in the art will appreciate that the functions described hereinmay be accomplished using one or more computing devices operatingtogether or independently. Those skilled in the art will also appreciatethat any suitable general purpose or specially programmed computer maybe used to achieve the functionality described herein.

[0031] Computer 40 is also operatively coupled to various control unitsincluding, for example, a gantry control 44 and a table control 48. Inoperation, computer 40 directs the movement of gantry 26 via gantrycontrol 44 and the movement of table 16 via table control 48. Thesedevices are controlled by computer 40 to place a patient in a properposition to receive treatment from the radiation therapy device. In someembodiments, gantry 26 and/or table 16 may be repositioned duringtreatment to deliver a prescribed dose of radiation.

[0032] Computer 40 is also operatively coupled to a dose control unit 50which includes a dosimetry controller and which is designed to control abeam source 52 to generate a desired beam achieving desired isodosecurves. Beam source 52 may be one or more of, for example, an electronand/or photon beam source. Beam source 52 may be used to generateradiation beams in any of a number of ways well-known to those skilledin the art. For example, beam source 52 may include a dose control unit50 used to control a trigger system generating injector trigger signalsfed to an electron gun in a linear accelerator (not shown) to produce enelectron beam as output. Beam source 52 is typically used to generate abeam of therapeutic radiation directed along an axis (as shown in FIG. 1as item 12) toward treatment zone 18 on patient 22.

[0033] According to one embodiment of the invention, the beam generatedby beam source 52 is shaped using one or more collimator assemblies,depending on the type of beam generated. For example, in one embodiment,a photon beam produced by beam source 52 is shaped by manipulating aphoton collimator 64, while an electron beam produced by beam source 52is shaped by manipulating an electron collimator 62. According to oneembodiment, photon collimator 64 and electron collimator 62 aremulti-leaf collimators having a plurality of individually-movableradiation blocking leaves. The leaves of each such collimator areindividually driven by a drive unit 58, 59 and are positioned under thecontrol of electron collimator control 54, photon collimator control 55and sensor(s) 56 and 57.

[0034] Drive units 58, 59 move the leaves of each collimator in and outof the treatment field to create a desired field shape for each type ofbeam. In one embodiment, where an electron beam is to be generated andprimary electrons are to be used in a treatment, photon collimatorcontrol 55 operates to retract individual leaves of photon collimator64, while electron collimator control 54 operates to position individualleaves of electron collimator 62 across the path of the electron beam togenerate a desired electron field shape at the isocenter. Similarly, inone embodiment, where a photon beam is to be generated and primaryphotons are to be used in a treatment, electron collimator control 54operates to retract individual leaves of electron collimator 62 whilephoton collimator control 55 operates to position individual leaves ofphoton collimator 64 across the path of the photon beam to generate adesired photon beam field shape at the isocenter. In other embodiments,both collimators 62, 64 may be controlled in concert during the courseof a treatment to generate a desired field shape at the isocenter.

[0035] Referring now to FIG. 3, a perspective view of portions ofradiation therapy device 10 is shown. In particular, FIG. 3 depictsportions of treatment head 24 as well as elements along a beam path 12.According to one embodiment of the present invention, treatment head 24includes an accessory tray 25 or other mounting device positionedbetween treatment head 24 and treatment area 18. Components of a photoncollimator (item 64 of FIG. 2) are shown as collimator blocks 90, 92 inFIG. 3. Collimator blocks 90, 92 are positioned within treatment head 24and may include a number of individual elements or “leaves” which may beindependently controlled to create a desired field shape at theisocenter. Any of a number of known collimators and shaping devices maybe used as photon collimator (item 64 of FIG. 2) in conjunction withembodiments of the present invention.

[0036] According to one embodiment of the present invention, a separateelectron collimator 62 is provided. According to one embodiment of thepresent invention, components of electron collimator 62 are removablymounted on accessory tray 25, allowing electron collimator 62 to bequickly installed and removed by radiation therapists or othertechnicians in order to add or remove electron field shapingcapabilities to a radiation therapy device. According to one embodiment,individual leaf beds consisting of a number of individual collimatorleaves 70 a-n are mounted on accessory tray 25 such that they can bemoved in a direction 72 across beam path 12. In one embodiment, theindividual leaves 70 a-n are formed of radiation attenuating materials.For example, brass or tungsten are currently preferred materials,although other materials with similar radiation attenuatingcharacteristics may be used. In one embodiment, individual leaves 70 a-nhave a width of approximately 1-2 cm. Those skilled in the art willrecognize that other shapes and sizes of individual leaves 70 a-n may beselected to produce different field shapes at treatment zone 18.

[0037] Collimator drives 58 a-n and other control circuitry are alsoremovably mounted on accessory tray 25. In one embodiment, collimatordrives 58 a-n and other control circuitry are mounted on an exteriorsurface of accessory tray, away from beam path 12, providing greaterdurability and length of service for the electrical components used tooperate electron collimator 62.

[0038] According to one embodiment of the present invention, a container80 (such as a balloon or the like) filled with helium is positionedalong a portion of beam path 12 to reduce the amount of free air alongbeam path 12. In one embodiment, container 80 is removably mounted toaccessory tray 25. By replacing some of the air in the air column withhelium (or another gas having a low density), the penumbra of theelectron beam is reduced, allowing greater control over the shape andeffect of the beam at the isocenter. In particular, use of helium alongbeam path 12 maintains the electron beam spread at a clinicallyacceptable level by decreasing the number of scattering interactions theelectrons experience before they reach treatment zone 18. In operation,a shaped electron field may be delivered to treatment zone 18 byretracting leaves of photon collimator blocks 90, 92, passing theelectron beam through helium-filled container 80, and selectivelyshaping the beam by manipulating electron collimator 62. Multiple fieldscan thus be delivered to treatment zone 18 during the course of atreatment without manual intervention. Further, embodiments of thepresent invention support mixed beam treatments by selectively switchingbetween electron and photon beams. According to embodiments of thepresent invention, manual intervention and equipment set-up is reducedor eliminated.

[0039] Applicants have found that mounting components of electroncollimator 62 on accessory tray 25 provides several desirable benefits.For example, during most types of treatments, electron collimator 62provides sufficient patient clearance in all gantry and table positions.Further, electronic components, such as collimator drives 58 a-n, willenjoy greater longevity because they are positioned away from beam path12. Additionally, greater accuracy is provided during treatment becausethe overall swing weight of treatment head 24 and accessory tray 25 areminimized. The inventive configuration also enjoys the advantage ofallowing ready removal and replacement of components. Accessory tray 25,in some embodiments, includes one or more accessory slots (not shown)into which components of electron collimator 62 may fit. In someembodiments, components of electron collimator 62 are installed bysimply inserting the components into one or more accessory slots ofaccessory tray 25. As a result, for treatments that require greaterclearance (e.g., such as photon treatments of breast cancer, etc.),components of electron collimator 62 may be readily removed, and thenre-installed as needed.

[0040] Placement of components of electron collimator 62 on accessorytray 25 also serves to reduce the electron penumbra at the isocenter,providing greater accuracy in the delivery of electron treatments. Thoseskilled in the art will recognize that the electron penumbra can bereduced further by positioning components of electron collimator 62closer to the isocenter; however, this increases problems withcollision. In some embodiments, additional collision detection andavoidance components may be utilized in radiation therapy device 10 toreduce collisions and to allow closer positioning of components ofelectron collimator 62.

[0041] Referring now to FIG. 4, details regarding the construction ofelectron collimator 62 are shown. FIG. 4 is a beams eye view of electroncollimator 62, showing the placement of container 80 in relation tocomponents of electron collimator 62. In one embodiment, electroncollimator 62 includes a plurality of individual collimator drives 58a-n each coupled to drive individual leaves 70 a-n of the collimator. Asdepicted, individual leaves 70 a-n may be positioned using collimatordrives 58 a-n to generate a desired collimator shape, thereby producinga desired electron field shape at the treatment area on a patient.

[0042] Those skilled in the art will appreciate that various adaptationsand modifications of the just described preferred embodiments can beconfigured without departing from the scope and spirit of the invention.Although a preferred embodiment utilizing removable electron collimatorcomponents has been described, in one embodiment, the electroncollimator components may be mounted in a manner that does notfacilitate ready removal. Therefore, it is to be understood that, withinthe scope of the appended claims, the invention may be practiced otherthan as specifically described herein.

What is claimed is:
 1. A radiation therapy device, comprising: aradiation source positioned to direct a beam along a beam path toward atreatment area; a treatment head containing a first collimatorcontrollable to selectively collimate said beam; and a second collimatorremovably positioned between said first collimator and said treatmentarea and controllable to selectively collimate said beam.
 2. Theradiation therapy device of claim 1, wherein said second collimator isremovably mounted on an accessory tray of said radiation therapy device.3. The radiation therapy device of claim 2, further comprising a firstcollimator drive and a second collimator drive, each said drive operableto selectively position individual leafs of said collimators.
 4. Theradiation therapy device of claim 3, wherein said second collimatordrive is removably mounted on said accessory tray.
 5. The radiationtherapy device of claim 4, wherein said second collimator drive ispositioned on an exterior of said accessory tray a distance from saidbeam path.
 6. The radiation therapy device of claim 1, wherein saidradiation source includes a photon radiation source and an electronradiation source.
 7. The radiation therapy device of claim 2, whereinsaid first collimator is controllable to selectively collimate a photonbeam generated by said photon radiation source.
 8. The radiation therapydevice of claim 2, wherein said second collimator is controllable toselectively collimate an electron beam generated by said electronradiation source.
 9. The radiation therapy device of claim 1, whereinsaid first and said second collimators are controllable to selectivelycollimate said beam.
 10. The radiation therapy device of claim 1,further comprising: a helium-filled container, positioned along saidbeam path between said beam source and said second collimator.
 11. Theradiation therapy device of claim 1, further comprising a control unitcoupled to said radiation source and to said first and said secondcollimator drives to selectively deliver a prescribed dose of radiationto said treatment area.
 12. The radiation therapy device of claim 11,wherein said control unit is operable to control said radiation sourceto generate a photon beam and to cause said second collimator drive toposition leaves of said second collimator away from said beam path todeliver a prescribed dose of photon radiation to said treatment area.13. The radiation therapy device of claim 11, wherein said control unitis operable to control said radiation source to generate an electronbeam and to cause said first collimator drive to position leaves of saidfirst collimator away from said beam path to deliver a prescribed doseof electron radiation to said treatment area.
 14. A radiation therapydevice, comprising: a control unit; a radiation source, controlled bysaid control unit to generate one of a photon beam and an electron beamalong a beam path toward a treatment area; a first collimator,positioned between said radiation source and said treatment area, saidfirst collimator selectively positioned by said control unit tocollimate said photon beam; and a second collimator, removably mountedbetween said first collimator and said treatment area, said secondcollimator selectively positioned by said control unit to collimate saidelectron beam.
 15. The radiation therapy device of claim 14, whereinsaid second collimator is removably mounted on an accessory tray of saidradiation therapy device.
 16. The radiation therapy device of claim 14,further comprising: a container positioned along said beam path betweensaid first and second collimators.
 17. The radiation therapy device ofclaim 16, wherein said container is filled with helium.
 18. Theradiation therapy device of claim 15, further comprising driveelectronics coupled between said control unit and said secondcollimator, said drive electronics mounted on an exterior of saidaccessory tray, and operable to position individual leaves of saidsecond collimator.
 19. A radiation therapy system, comprising: a controlunit; a treatment head having an enclosed area and an accessory tray; aphoton radiation source, selectively operated by said control unit togenerate a photon beam along a beam path from said treatment head towarda treatment zone; an electron radiation source, selectively operated bysaid control unit to generate an electron beam along said beam path fromsaid treatment head toward said treatment zone; a photon collimator,located between said photon radiation source and said treatment zone;and an electron collimator, removably mounted on said accessory tray,said electron collimator selectively positioned by said control unit tocollimate said electron beam.
 20. An electron collimator for use incollimating an electron beam in a radiation therapy device, thecollimator comprising: drive electronics, removably mounted on anexterior of an accessory tray of said radiation therapy device; and aplurality of leaves positionable by said drive electronics to moveacross a path of said electron beam, said plurality of leaves removablymounted on said accessory tray of said radiation therapy device.
 21. Aradiation therapy device, comprising: a radiation source positioned toselectively direct an electron beam and a photon beam along a beam pathtoward a treatment area; a treatment head containing a first collimatorcontrollable to selectively collimate said photon beam; and a secondcollimator positioned between said first collimator and said treatmentarea and controllable to selectively collimate said electron beam.
 22. Aradiation therapy method, comprising: operating a radiation source todirect a beam from a treatment head along a beam path toward a treatmentarea; selectively controlling a first collimator to collimate said beam;selectively controlling a second collimator to collimate said beam, saidsecond collimator removably positioned between said first collimator andsaid treatment area.
 23. A radiation therapy method, comprising:selecting between an electron treatment beam and a photon treatmentbeam; directing said selected beam from a radiation source along a beampath toward a treatment area; selectively controlling a first collimatorto collimate said selected beam if said selected beam is said photonbeam; and selectively controlling a second collimator to collimate saidselected beam if said selected beam is said electron beam, wherein saidsecond collimator is positioned between said first collimator and saidtreatment area.